1. Field of the Invention
The present invention relates to a structure and a method for mounting a semiconductor element, and more particularly to a structure and a method for mounting a semiconductor element which use indium as conducting adhesive.
2. Description of the Prior Art
In a chip-type semiconductor device or the like which incorporates a semiconductor element, the fixing of the semiconductor element on an electrode formed on a chip substrate is achieved by applying indium, which acts as conducting adhesive, to the electrode, then placing the semiconductor element on top of it, and then heating the indium to melt it and then cooling it to solidify it. FIG. 3 shows a conventional mounting structure. First, by the use of a pin 7, molten indium 6 is applied to the surface of an electrode 2 formed on a chip substrate 1((a) in FIG. 3). The molten indium 6 applied to the electrode 2, under its surface tension, forms a drop, making a certain angle xcex8 with the electrode 2((b) in FIG. 3). Next, a semiconductor element 4 is placed on the molten indium 6((c) in FIG. 3). Then, the molten indium 7 is cooled so as to be solidified. In this way, the semiconductor element 4 is mounted on the electrode 2((d) in FIG. 3).
However, in this conventional mounting structure, it is difficult to precisely control the amount of indium applied to the electrode, causing the indium to be applied to the electrode in an insufficient amount sometimes and in an excessive amount other times. In a case where the semiconductor element is a light-emitting element, an excessive amount of indium applied to the electrode causes the indium to attach not only to the bottom surface of the semiconductor element (light-emitting element) 4 but also to its side surfaces, shutting off part of the light emitted by the light-emitting element 4 and thus lowering light emission efficiency. With a light-emitting element such as a ZnSe-based light-emitting element which produces white light by emitting light in two colors, indium attached to its side surfaces, by shutting off part of the emitted light, upsets the balance of the two colors and causes variations in the resulting hue.
An object of the present invention is to realize secure mounting of a semiconductor element on an electrode through precise control of the amount of indium applied to the electrode.
Another object of the present invention is to realize, in a case where a light-emitting element is dealt with as a semiconductor element, fixing of the light-emitting element on an electrode without loss in light emission efficiency or variations in the hue of the emitted light.
To achieve the above objects, according to the present invention, in a structure for mounting a semiconductor element, the semiconductor element is fixed with an indium film that is formed on an electrode by plating. This structure permits precise control of the amount of indium applied to the electrode, and thus permits secure mounting of the semiconductor element on the electrode. By preparing beforehand a substrate having an indium film formed in a predetermined position on an electrode and then mounting a semiconductor element on that substrate, it is possible to eliminate the process of applying indium when a semiconductor element is mounted as required conventionally, and thereby increase working efficiency in the semiconductor element mounting process.
Here, to minimize loss in the light emission efficiency of the light-emitting element and variations in the hue of the light it emits, the indium film has a thickness preferably in the range from 5 to 10 xcexcm.
To achieve the full effect of the mounting structure of the invention, the semiconductor element is preferably a ZnSe-based light-emitting element.
To ensure secure and economical fixing of the semiconductor element on the electrode with the indium film, the indium film formed on the electrode has an area preferably in the range from 1.1 to 1.5 times the area of the surface over which the semiconductor element is fixed.
To achieve the above objects, according to the present invention, a method for mounting a semiconductor element includes the steps of forming an indium film on an electrode by plating, placing a semiconductor element on the indium film, and melting and then solidifying the indium film so that the semiconductor element is fixed on the electrode. This method permits precise control of the amount of indium applied to the electrode, and thus permits secure mounting of the semiconductor element on the electrode.
Here, to obtain the desired thickness efficiently, the plating is achieved preferably by electroplating.
For quick and secure fixing of the semiconductor element with the indium film, the fixing is achieved by means of at least one of heat, supersonic vibration, and mechanical vibration.